Dario Saric scored key baskets to extend the lead and bolster his bid for NBA Rookie of the Year. Saric scored 23 points and helped rally the Sixers from a 13-point hole in the third.

"I think the toughness and determination that they repetitively show isn't a fluke, it's who they are," coach Brett Brown said.

Covington buried a 3 with 3:37 left that put the Sixers up 94-91 and Nik Stauskas hit his own with 38 seconds left for a 103-97 lead that sent fans inside a packed Wells Fargo Center into a frenzy.

The Sixers thumped Dallas 116-74 on Friday night and improved to a respectable 17-19 at home. The Sixers won 10 games total last season.

The Celtics, still with a nice lead in the Atlantic Division, won the first three games of the season against the Sixers.

"Finally, we beat them," Saric said.

Al Horford led the Celtics with a season-high 27 points in a game Boston could not afford to waste.

Boston guard Isaiah Thomas sat out a second straight game with a bone bruise on his right knee and was questionable for Monday's game at Washington. The Celtics could surely use their leading scorer (29.2 points) against the Wizards. Boston and Washington are jostling for a top three seed headed into the Eastern Conference playoffs.

Horford came up empty in the clutch with a scoreless fourth.

"Guys are really looking for me. I'm just trying to make plays," he said.

Just not enough of them.

Saric waved his arms told the crowd of 19,446 and urged them to get louder down the stretch of Philadelphia's fantastic comeback. Jahlil Okafor, the No. 3 overall pick in the 2015 draft, sat out the second half for the Sixers because of right knee soreness.

The Sixers were just fine without him.

Jae Crowder, who scored 15 points, kept Boston in the game with a couple of late clutch 3s that never should have been necessary.

Philadelphia's rebuilding continues to take small steps as it overcomes injuries to its core players. Brown admired the way the Celtics have used smart drafts, trades and free-agent deals to rise and become a force in the East.

"I think there's a lot to be learned from them," he said. "I look at them as one of the teams in the Eastern Conference that is very, very dangerous."

Covington scored 23 points. Saric made 10 of 20 baskets and added six rebounds and four assists.

TIP-INS

Celtics: Marcus Smart scored eight points starting for Thomas. ... Horford had averaged 13.6 points and 8.7 rebounds in 27 career games against the Sixers. ... Horford said the Celtics have no choice but to "regroup." "We have a tough one at home."

Sixers: Brown said a healthy Joel Embiid and Ben Simmons, the No. 1 overall pick of the 16 draft, along with Saric give the Sixers the kind of core that could help them become the next Boston. "I'm extremely comfortable with our base," he said. "I look at this year's team as a team that has far more capable bodies and players that can move forward next year as a cultural piece, as a corporate knowledge piece." ... G Justin Anderson (gastroenteritis) sat out.

HE SAID IT

Brown said the win was extra satisfying because the Celtics are one of the top teams in the NBA and should make a deep playoff run.

"With the group that we have, there is zero margin for error. Almost," he said. "Especially against a team that has a chance to play in the Eastern Conference championship."

UP NEXT

Celtics: Return home Monday to play Washington.

Sixers: The Sixers start a five-game road trip Monday at Orlando. The Sixers also play Oklahoma City, Chicago, Indiana and Brooklyn.